Arteriosclerosis is a condition in which plaques develop on the inner walls of blood vessels and restrict the flow of blood therethrough. Organs downstream of this constriction can be starved of oxygen, and the heart must work harder to pump blood through a circulatory system that includes such blockages. When the blockage occurs in the coronary arteries which feed the heart, a heart attack can result. Similarly, blockages in the carotid arteries can restrict the flow of blood to the brain with obvious negative consequences.
These blockages are often found in locations that are difficult to access. For example, the coronary arteries and some portions of the carotid arteries are protected by the rib cage. At one time, major surgery was required to reach these locations. However, several methods have been developed for treating plaques in these areas, which methods involve the insertion of a catheter into a patient""s blood vessel at a location that is easy to reach, and guiding the catheter through the vessel toward the blockage, such as lasers of other cutting tools. However, one of the more common tools is a balloon which is placed in the constricted area of the vessel and inflated once or a number of times in order to push the plaque back against the arterial wall to open the artery. This procedure is called balloon angioplasty and is a common treatment for arteriosclerosis today.
In order to get a balloon to the location of the blockage, a catheter must be placed into a patient""s artery. This is done by inserting a needle into an easily accessible artery and threading a guide wire through the needle and into the patient""s artery. The needle is withdrawn over this guide wire and an arterial sheath is place over the needle and into the artery to protect the artery and surrounding tissue during the procedure. A guiding catheter is placed over the guide wire and maneuvered through the artery to a position near the site of the blockage. When the end of the guiding catheter arrives at a location near the blockage, the guide wire is removed, and the catheter is flushed with saline and anchored in place in a suitable manner. A balloon catheter, having an associated guide wire is then inserted into the guiding catheter and pushed through the catheter, out of the distal end of the catheter, and guided to the site of the blockage. The guide wire is pushed past the blockage and the balloon is positioned within the blockage and inflated to compress the buildup in the artery. When the procedure is complete, the balloon catheter is removed from the guiding catheter and then the guiding catheter is removed as well. This procedure has had a high success rate and is the preferred method for treating certain types of blockages.
One of the dangers associated with this procedure is that a part of the plaque could break off and enter the patient""s blood stream during treatment. While no part of the plaque is actually cut away during a balloon angioplasty procedure, small pieces of plaque known as micro-emboli can and do sometimes break free These materials are often too large to pass easily through the body""s capillaries and can become lodged therein and block the flow of blood. If the blockage occurs in the brain or the lungs, it can be harmful or even fatal. Therefore, a variety of techniques are used to stop these particles before they travel too far.
Heretofore, various filters have been used to trap these particles. Some, such as the filter disclosed in U.S. Pat. No. 4,873,978 to Ginsburg comprise a wire mesh for straining objects from the bloodstream. However, this strainer must be inserted into a blood vessel through its own opening, downstream from the treatment site and separate from the opening used for the balloon catheter or similar device. This makes this filter difficult to use and creates additional discomfort for the patient. Others, such as the filter shown in U.S. Pat. No. 4,425,908 to Simon are intended to be permanently attached to the inner wall of a blood vessel. However, it is often desirable to remove the filter after a procedure is complete, and this would not be practicable using the Simon filter. In addition, the wire mesh strainers disclosed in these patents might be capable of stopping relatively large pieces of material, such as those generated when a plaque is severed from an arterial wall by a cutting instrument, but are not suitable for stopping the micro-emboli that can occur during a balloon angioplasty procedure. Neither these nor any other known devices provide a simple and effective option for dealing with such micro-emboli while at the same time functioning to block any larger pieces of material that might break free. It would therefore be desirable to provide a blood filter for trapping micro-emboli that could be deployed immediately before a procedure was commenced and removed shortly thereafter and which could be inserted and removed through the same catheter used in connection with the procedure.
The present invention overcomes these and other problems by providing a compact filter for use alone or as part of an apparatus for performing a balloon angioplasty. The filter comprises a rod slidingly housed within a catheter, and a plurality of curved, flexible wires longitudinally disposed along the rod and connected thereto at two spaced apart locations. A portion of filter material is supported by the wires. When the rod is inside the catheter, the wires are held in close proximity to the rod by the walls of the catheter. When the rod is extended from the catheter, the wires resume their preformed, curved shape and curve away from the rod. This stretches the filter material across the passageway to trap any plaques or clots that are present. When the need for filtration is ended, the rod is pulled back into the catheter. This process compresses the wires against the rod and closes the filter material around any trapped materials so that they can be removed from the body.
In a preferred embodiment of the invention, the flexible wires are attached to two connectors on the outer surface of the rod. The connectors are ring-shaped and the wires are evenly distributed about the circumference of the rings. The connector closest to the distal end of the rod (the end inside the patient""s body) is slidably connected to the rod while the proximal connector is fixed. The wires are preformed in a curved shape such that when unbiased by the walls of the catheter, they extend from the proximal connector through an arc that takes them away from the rod and then back toward the distal connector where they are also attached. The volume defined by the wires is generally ovoid, and the largest diameter of the volume perpendicular to the axis of the rod is selected to be about equal to the diameter of the blood vessel in which the filter is to be used. Because the wires are flexible, and because the distal connector can slide relative to the rod, when the rod is pulled into a catheter, the wires are compressed toward the rod and the distal connector is slid along the rod away from the proximal connector. When the rod is pushed out of the catheter, the distal connector slides toward the proximal connector and the wires resume their preformed shape.
A filter element is attached to the wires to trap material that comes loose from the arterial walls during a procedure. In the preferred embodiment, two layers of a biocompatible material, such as Gortex brand fabric, are used as the filter element with one layer attached to the side of the wires facing the rod and the other attached to the opposite side so that the wires are sandwiched in-between the two layers. The material extends from the distal connector toward the midpoint of the wires or even slightly further toward the proximal connector. Each layer includes small perforations to allow fluids to pass while trapping even very small emboli. The perforations on the inner sheet are offset from those on the outer sheet to better trap and retain emboli. The material is pulled inwardly toward the rod by the wires when the rod is retracted into a catheter and is thin enough to fold easily.
The filter can be inserted by itself, but preferably, it is carried on the same rod used to hold a balloon for a balloon angioplasty procedure. In use, therefore, the balloon catheter will be guided through an arterial narrowing so that its distal end extends beyond the narrowing and so that the balloon is positioned within the narrowing. The rod is then extended from the catheter to push out the filter a distance of about 1 millimeter. After the balloon has been inflated and deflated to enlarge the passageway, the rod and filter are pulled back into the catheter and the catheter is removed from the body.
The filter also includes safety features to prevent parts of the filter itself from breaking off of the rod. A stop is included on the distal end of the rod which will prevent the slidable connector ring from sliding all the way off of the rod in the unlikely event that the wires holding it to the proximal connector should be broken. In addition, a safety wire is attached between the proximal connector and the distal connector, as well as to the midpoint of the rod therebetween. This wire limits the movement of the distal connector in both directions along the rod. By preventing the distal connector from moving too far in a distal direction, it prevents the other wires extending between the connectors from being stressed. By preventing the distal connector from moving too far in the proximal direction, it limits the diameter of the ovoid volume defined by the curved wires so as not to damage the vessel walls that surround the filter.
It is therefore a primary object of the present invention to provide an apparatus for filtering a fluid in a bodily passageway.
It is another object of the present invention to provide a filtering device for filtering blood flowing through a blood vessel.
It is a further object of the present invention to provide a collapsible filtering device which can be passed through a narrowing in a blood vessel and then expanded to its functional size on the other side of the narrowing.
It is yet another object of the present invention to provide a filtering device which can be inserted into a blood vessel through a catheter.
It is yet a further object of the present invention to provide a filtering device that can be attached to an instrument used during an angioplasty procedure.
It is still another object of the present invention to provide a filter suitable for trapping both large and small particles of material in the bloodstream.
It is still a further object of the present invention to provide a filtering device that can be deployed and retracted in a simple manner from a remote location.
It is yet another object of the present invention to provide a filter for use in conjunction with a catheter which filter is shifted between functional and storage configurations by sliding it into and out of the catheter.
It is another object of the present invention to provide a filter that can be deployed and retracted by sliding the filter support relative to a tubular member such as a catheter.
It is yet another object of the present invention to provide a filtering apparatus that includes safety features to help prevent portions of the apparatus from separating from the apparatus.